Transfer images, wherein the image retained on a material is the mirror image of the original object, can be obtained in many ways. Traditionally, transfer images have been made by inking or otherwise coating the original object, and placing the object against a receptive material, such as paper, canvas, cardboard, cloth, or the like, wherein the receptive material becomes imprinted with the mirror image of the object.
For example, a fingerprint can be acquired by pressing a finger onto an inked surface, and pressing the inked finger against a receptive or imaging sheet. U.S. Pat. No. 6,298,805 discloses ink and an inking apparatus for taking fingerprints. In fingerprinting, or any image transfer, after inking, the object, for example, the finger, must be applied to the receptive sheet accurately to provide a good image. The application must be made smoothly, with even pressure, and without movement of the object relative the receptive sheet, or smearing will occur. Errors made in capturing the image require use of a new receptive sheet and re-inking of the object. After image capture, the object must be cleaned, which is often messy and time consuming. The entire image capture process requires multiple steps, is messy, and is prone to error.
Electronic means have been proposed for capturing fingerprints. U.S. Pat. No. 6,784,413 discloses optical means for capturing an image of a fingerprint. U.S. Pat. No. 7,592,264 discloses an electronic sensor responsive to pressure that can capture a fingerprint pattern digitally. An additional apparatus, such as a printer, is required to convert the digital data into a print of the fingerprint. Forming a print in this manner requires two separate apparatuses, as well as media for the printer.
Various electrically responsive materials are bistable, meaning that they are capable of retaining an image in the absence of power. Such materials are being used to provide field-stable, re-writable displays. The materials can be capable of changing optical states in response to applied energy in the form of electricity, magnetic field, heat, or light.
U.S. Pat. No. 3,789,225 discloses a method of forming an image on a display including glassy cholesteric liquid crystal material between glass plates. Glassy liquid crystal materials are solidified liquid crystals in an orderly state at ambient temperatures. They are not responsive to electrical fields in the glassy state. The method for forming the image includes writing the display to an initial state by heating the liquid crystal material above a transition point, cooling the material, and applying a high-intensity xenon flash lamp image-wise to the cooling material so that the flashed areas solidify into a state different than areas not receiving flash energy.
Non-glassy liquid crystals can be electrically driven between a planar state reflecting a specific visible wavelength of light, and a light scattering focal-conic state, at ambient temperatures. Chiral nematic liquid crystals, also known as cholesteric liquid crystals, are bistable. U.S. Pat. No. 5,437,811 discloses a light-modulating display including a polymer dispersed chiral nematic liquid crystal that is capable of changing optical states in the presence of an electric field, and maintaining a given optical state in the absence of the field.
U.S. Pat. No. 6,740,255 discloses a photo-responsive liquid crystal composition that is capable of recording an image-wise pattern in response to ultra-violet light. The image can be erased by heating.
The above methods of image capture using bistable materials require expensive and complex photosensitive layers for operation, complex electrical drive systems for writing data sequentially, or both. Contact printing systems known in the art can require more than one apparatus, such as an image-capture device and printer, to reduce the image to a printed form, and can be messy and time consuming.
There is a need for a simple and clean method of producing a transfer image. It is desirable that such an image be rewritable should an error occur in image capture. It is further desirable that the image capture apparatus and imaging material be simple to operate and portable.